Sjöberg, Göran

Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.

1993 (English)Doctoral thesis, comprehensive summary (Other academic)

Abstract [en]

The aim of the thesis was to document patterns in breeding and migration in Swedish Canada geese Branta canadensis, to explain these against the genetic and historical background of the population, and to test predictions of hypotheses pertaining to parental investment.

The Canada goose population in Sweden was founded by the introduction of a few individuals in the 1930's. DNA fingerprint similarity between geese breeding in Sweden was on average at the same level as between inbred close relatives in other wild bird species. The genetic variability of the population appeared to be considerably reduced in comparison to that of Canada geese breeding in North America.

Dispersal and migration patterns were studied using plastic neck-bands that could be identified at long distance. Most Canada goose females nested at the lake where they grew up. Males were more prone to disperse than females, although most of them still returned to breed close to their area of origin.

Geese from three breeding areas in Sweden had different winter distributions, although wintering areas overlapped considerably. Individual geese tended to return to the same wintering area as they had used in previous years.

The females' investment in the egg clutch was related to the migration distance from spring foraging areas to the nesting area, suggesting an energetic cost of migration for egg production. Within breeding seasons, clutch size decreased with later initiation of nesting, but only in years with early breeding. A probable reason for this decrease was that body reserves available for egg production were larger in early layers. In years with late breeding, clutch size did not decrease, most likely because late-nesting females could supplement their body reserves by foraging on fresh vegetation.

Nest defence intensity was studied by recording the behaviour of the female geese when a human approached the nest. The results largely confirmed predictions for nest defence intensity extracted from parental investment theory.